Circuit breakers provide automatic current interruption to a monitored circuit when undesired fault conditions occur. These fault conditions include, for example, arc faults, overloads, ground faults, and short-circuits. As is well-known, a circuit breaker is an automatically operated electromechanical device designed to protect branch wiring from damage caused by an overload or a short circuit. A typical circuit breaker has a load connector and a power connector with a break mechanism interposed between the load connector is (connected to a load device) and the power connector (connected to a power source such as a panel board). Various fault conditions trip the circuit breaker thereby interrupting power flow between the load and the power source. A circuit breaker can be reset (either manually or automatically) to resume current flow to the load.
An overcurrent may be detected when the fault current generates sufficient heat in a strip composed of a resistive element or bimetal to cause the bimetal to deflect and/or bend. The mechanical deflection triggers a trip assembly that includes a spring-biased trip lever to force a moveable contact attached to a moveable conductive blade away from a stationary contact, thereby breaking the circuit. When the circuit is exposed to a current above that level for a predetermined period of time, the trip assembly activates and tripping occurs thereby opening the circuit.
A circuit breaker may also include a solenoid coupled to electronic components that detect one or more fault conditions such as an arc fault in branch wiring or cord sets and are operable to cause the circuit breaker to electronically trip. The solenoid and the electronic components may be provided in addition to or in lieu of the thermal-magnetic tripping components. The electronic components process a signal output of a sensor that monitors current flowing in the circuit breaker. The electronic components may be configured to determine whether one of the fault conditions is present and to generate a fault signal and/or a trip signal. In response to the generation of a fault signal, a magnetic field is created around the solenoid, causing a plunger to move an armature relative to a yoke, which triggers a chain of mechanical actions that cause the circuit breaker to electronically trip.
The data on what fault conditions were present to trigger the trip condition is useful for fault diagnosis. Thus, a circuit breaker ideally includes an indication of the condition that leads to the tripping of the circuit breaker. However in many current mechanical or electrical circuit breaker designs, the event that led to the trip condition is not indicated by the circuit breaker. Thus, fault diagnosis is complicated by the lack of information to assist a technician.
One proposed solution uses light emitting diodes (LEDs) to indicate the cause of the trip condition. However, this solution requires the power to be enabled to the electronics of the circuit breaker in order to power the LEDs to display the causes of a trip condition. However, this requires power to be restored to power the LED fault display. Such restored power is also supplied to the load side terminals creating a potential hazard since the cause of the fault may still be connected to the load side terminals. Further, the fault condition must be stored in the memory of the circuit breaker thus taking up memory space.
The current circuit breaker designs therefore suffer from a problem of not having any indication of the fault that caused a tripped state when the power is turned off.